The present invention relates to an improved structure of a capacitor, in particular, relates to the improved structure of a chip type ceramic capacitor.
A chip type capacitor comprises of a dielectric block, a pair of conductive electrodes embedded in the block or provided on the surface of the block, and a pair of terminals at opposite ends of the block. A chip type capacitor has the advantages that the size is small, a large capacitance is obtained in a small size of capacitor, the high density of mounting on a printed circuit board is possible by bonding the chip type capacitor on a flat conductive pattern, the high frequency operation is superior, and the external shape is common. Therefore, the automatic assembling and/or the automatic mounting of a capacitor is possible. Accordingly, a chip type capacitor is used in electronics appliances including miniature radio sets, tape recorders, an electric calculators, and/or electronic tuners in television sets, and the amount of capacitors utilized in those electronics appliances is increasing rapidly.
FIGS. 1A and 1B show a structure of a prior chip type capacitor. In those figures, a dielectric body 1 which is 50-100.mu. of thickness made of Barium-titanate or titanium oxide, has a pair of electrodes 2 and 3 on both the surface of said dielectric body 1. A pair of terminals 4 and 5 are provided at opposite ends of the block 1 so that those terminals 4 and 5 are electrically connected to the electrodes 2 and 3, respectively. The reference numeral 6 is a protective layer made of glass or plastics provided on the surface of the electrodes 2 and 3 for improving the insulation and to resist against the chemical corrosion of electrodes 2 and 3.
FIGS. 1A and 1B show the embodiment of a trimming capacitor in which a trimming electrode 2 is trimmed for fine adjustment of the capacitance through trimming by sandblastes, a diamond cutter, or a laser beam. However, other types of chip capacitors are of course possible, like a single layer type capacitor having a dielectric body and a pair of electrodes embedded in the dielectric body, a laminated layer type capacitor having a dielectric body and laminated electrodes in said body, and/or a fixed type capacitor which is not trimmed.
FIGS. 2A and 2B show a part of the manufacturing process of a chip capacitor. First, the structure as shown in FIG. 1A is prepared. In FIG. 1A, electrode patterns 2, 2a and 3 are attached on the surface of the dielectric body 1. Next, the terminal 4 is provided on the side of the dielectric body 1 by painting silver paste with a brush so that the terminal 4 or the silver paste is electrically connected to one of the electrode patterns. Similarly, the other terminal (not shown) is painted on the opposite side of the dielectric body so that the terminal is electrically connected to the other electrode pattern. Finally, the whole body is sintered or heated in a furnace.
However, a prior chip capacitor has the disadvantages as described below.
When silver paste is painted on a capacitor assembly shown in FIG. 2A, there is the tendency that the thickness of the paint at an edge of the dielectric body is thin. Therefore, in order to provide the sufficient thickness at an edge portion, the painting is repeated several times. However, in the repetition of the painting, the portion except the edges is also painted inevitably. Therefore, the thickness of the silver paste at the portion A near the edge becomes thicker than the other portion B as shown in FIG. 3A. Further, since the silver paste is painted by a brush, the thickness of the paste is not always constant. And since the thickness t.sub.1 of a chip capacitor is usually very thin, and is around 1 mm, the ratio of the thickness of the silver paste to the entire thickness of a capacitor (t.sub.1) is rather large.
Accordingly, when a plurality of chip capacitors are arranged in line on a plane, or stacked in the magazine 100 as shown in FIG. 3B, the terminals disturb the easy handling of chip capacitors. In particular, a prior chip capacitor has the disadvantages that the automatic production of a chip capacitor is difficult, and the automatic mounting of a chip capacitor on a printed circuit board is also difficult. In particular, when chip capacitors are secured or stacked in the magazine 100 as shown in FIG. 3B, the number of chip capacitors stacked in the magazine 100 is reduced because of the thick terminals, thus, the efficiency for automatic mounting of capacitors on a printed circuit using a magazine is reduced. Further, since the thickness of terminals is not always constant, the stability of mounting capacitors when stacked in a magazine is bad, and the trouble occurs frequently when an automatic mounting of a capacitor to a printed circuit board is carried out.
Further, since the painted terminals have the large portions p, q, r and s at the corners of the half assembly as shown in FIG. 3C, the size of a magazine for stacking capacitors must be enough to hold those large portions. However, the size of those large portions are not always constant because of the painting, the size of a magazine must be large enough to hold even when those large portions are the maximum size. Therefore, when those large portions are medium sized, an inevitable air gap is provided between a capacitor and the inner wall of a magazine, and a capacitor can not be stacked tightly in a magazine. The loose stacking of a capacitor in a magazine causes trouble when an automatic mounting of a capacitor on a printed circuit board is carried out.
Another disadvantage of a prior chip capacitor is that the structure is mechanically weak and is easily broken, since the thickness of a capacitor is thin.
Still another disadvantage of a prior chip capacitor is that the error of the capacitance is relatively large due to the error in the manufacturing process.